Remark 2.2 Here, we emphasize that if \(u\) , \(\rho \)  satisfy one of the stationary HS2 equations
in
\((\ref {2.34})\)  for a particular value of \(n\) , then they satisfy infinitely many such equations
of order higher than \(n\)  for certain choices of integration
constants \(c_l\) . This is a common characteristic of the general
integrable soliton equations such as the KdV, AKNS, and CH
hierarchies [1]}.

